Photoballistics of volcanic jet activity at Stromboli, Italy

Abstract

Volcano Stromboli, Italy, has been in a nearly continuous state of activity since the earliest records were made by Aristotle. Well‐collimated jets of incandescent gases loaded with basaltic vitric lapilli characterize these eruptions, for which the term strombolian activity has been coined. We report results of a photographic study of two eruptions, one relatively large and one small, using principally high‐speed movies taken with a Hulcher 102 (70‐mm) camera at a rate of 10 frames/s and exposure time of 1/72 s. Ninety‐six frames, containing about 13,000 streaks, were analyzed with a computer interfaced digital film reader yielding detailed data on the bulk and time‐dependent properties of these two eruptions. We believe that these two eruptions bracket typical conditions at Stromboli; hence the results can be taken as representative of strombolian activity at the type locality. Geometric ambiguities, data acquisition, and reduction problems are discussed. Results for the two eruptions were as follows: duration of eruptions, 8 and 5 s; number of particles ejected, 2594 and 152; average (and maximum) particle size, 2.2 (31.8) and 2.5 (13.5) cm; average (maximum and minimum) particle velocity, 26.2 (2.5–72) and 15.3 (4.5–38) m/s; median angular dispersion from the jet axis, 8° and variable (10°–45°); mass of particles ejected, 100 and 7.6 kg; total kinetic energy of particles, 16.2 and 2.5×1010 ergs; calculated possible range of gas density, 0.05–0.30 mg/cm3 for both eruptions; maximum gas velocity, 112 and 94 m/s; calculated mass of gas ejected, 240 and 120 kg; and gas to lava mass ratio, 2.4 and 15.8. Particle velocity and calculated gas velocity decayed from their initial maximum values, but well‐marked oscillations with a period of about 1.6 s were superimposed. One model explaining these fluctuations is organ pipe resonance implying a tube length of 300–400 m. We estimate the flow to be subsonic, with a Mach number of 0.2–0.3. The range of estimated gas density is consistent with mixtures of CO2 and H2O.

Icelandic pseudocraters as analogs to some volcanic cones on Mars

“…Ejection angles of 60 ø to 50 ø produce ejection ranges 40 to 65% greater than an angle of 70 ø . In any given explosion, some proportion of material might be ejected at angles lower than 70 ø which would contribute to the outer apron, but most material comprising the inner cone is ejected within a narrow range of angles [Chouet et al, 1974].…”

Recycled ejecta modulating Strombolian explosions

“…James et al 2004James et al , 2006James et al , 2008Lane et al 2013), and field observations (e.g. Chouet et al 1974;Blackburn et al 1976;Ripepe et al 1993Ripepe et al , 2005Patrick et al 2007;Harris et al 2012;Taddeucci et al 2012a, b;Gaudin et al 2014;Bombrun et al 2015).…”

Rapid hazard assessment of volcanic ballistic projectiles using long-exposure photographs: insights from the 2010 eruptions at Tungurahua volcano, Ecuador

“…The coordinates of five points from each trajectory are extracted using the point tool on ImageJ. This information is completed with the width of the trajectories, measured with the segment tool, that allows to estimate the apparent maximum diameter of the projectiles [Chouet et al 1974]. The position of the lowest projectile impact and rolling block can also be extracted from the photograph.…”

“…The problem is that this resolution is feasible only if the vent is close enough to measure angle difference between the two cameras or if the cameras are located far away which is logistically difficult. In order to calculate the ballistic velocities Chouet et al [1974] use the length of the ballistic traces on very short exposures. In the present study I use the characteristics of the ballistic trajectories and resolve their polynomial equations in order to extract the volcano-physical data.…”

“…In Ecuador, two volcanologists from the Instituto Geofísico de la Escuela Politécnica Nacional, Victor Hugo Pérez and Álvaro Sanchez, died from a phreatic explosion in March 12th 1993. This hazard is mainly studied through field work on impact craters and deposits [Alatorre-Ibargüengoitia et al 2012;Maeno et al 2013] and/or monitoring (punctual or continuous) at currently active volcanoes [Chouet et al 1974;Ripepe et al 1993;Hort and Seyfried 1998;Dubosclard et al 2003;Andronico et al 2008;Gouhier and Donnadieu 2011;Taddeucci et al 2012b;Dürig et al 2015]. Hazard assessment is generally completed with numerical simulations that require a large number of eruptive source parameters: the projectiles properties (size, density and shape), the atmospheric conditions (temperature and pressure at different altitude, speed of tailwind), the explosion characteristics (launching velocity and angle, extent of reduced drag zone), and the local topography [Mastin 2001].…”